Regulating apparatus



g- 29, 1961 c. B. SHIELDS ETAL 2,998,514

REGULATING APPARATUS 2 Sheets-Sheet 1 Filed Jan. 3, 1956 m SN @QQQBQFN aallzipalfw v QR @QMBQQQ aaampaazu INVENTORS. Glmrles B. Shields and Q w \m m 5 s 1 a N N kmiwwuwmw \mxmwmagk w HUM W @W x AS m N NA MM IQ m: Q

Philip [1 Lui'z Y B a 4 \Sf;

THEIR ATTUH/VE Y United States Patent 2,998,514 REGULATING APPARATUS Charles B. Shields and Philip H. Luft, Penn Township, Pa., assignors to Westinghouse Air Brake Company, Wllmerding, Pa., a corporation of Pennsylvania Filed Jan. 3, 1956, Ser. No. 557,034 4 Claims. (Cl. 246-64) Our invention relates to regulating apparatus and more specifically to a regulating means suitable for use in controlling the length of certain forms of track circuits employed in railway signaling systems.

One form of track circuit which has recently been developed is usually referred to as an audio frequency overlay track circuit. A track circuit of this type comprises a transmitter having its output circuit connected to the rails of a section of railway track for the purpose of supplying energy thereto, and a receiver having its input circuit connected to the same rails for the purpose of detecting the presence in the track rails of the energy supplied thereto by the transmitter. The effective track circuit length is a function of the frequency of the energy supplied to the rails, the transmitter power output, the receiver sensitivity, rail impedance, and circuit attenuation. A track circuit of this type has an advantage over existing forms of track circuits in that it can be superimposed over existing track circuits without mutual interference and without the need for insulated rail joints for restricting its length.

In an overlay track circuit, rails may be conducted by the rails along the track in both directions. The receiver and transmitter may be connected to the rails at a common location or they may be separated a short distance. In the latter case, the distance is such that the receiver can be energized with energy received from the transmitter and with the frequencies usually employed this distance is approximately 300 feet.

When a train approaches the audio frequency overlay track circuit, the wheels and axles of the train form a series circuit with the track rails to provide a shunt across the receivers input circuit. However, the track rails have a relatively high impedance in comparison to the impedance of the Wheels and axles. The high rail impedance prevents the energy received by the receiver from being reduced sufficiently to indicate the presence of a train until the train has approached to within a short predetermined distance of the audio frequency overlay track circuit.

An increase in either the transmitter power output or the receiver sensitivity increases the distance along the track within which a train can be detected, whereas a decrease in either of these quantities decreases the distance within which the train can be detected. It is therefore obvious that these quantities must be regulated if the efieotive track circuit length is to be maintained constant.

The transmitter and receiver developed for this'purpose employ transistorized circuitry, and like most transmitters and receivers, the transmitter power output and receiver sensitivity depend upon the voltage of their direct current supply sources. It is, therefore, necessary to employ some means for regulating the direct current supply potential. However, the usual and well known techniques, such :as voltage regulator tubes and the like, are undesirable for use with transistor circuits due to the relative high voltages necessary for their operation in comparison with the required operating potentials for transistors. For this reason, a new and novel regulating means has been developed for use with such circuits.

Accordingly, an object of our invention is the provision of a regulating means suitable for use with an overlay the energy supplied to the track circuit which will maintain the transmitter power output substantially constant and independent of voltage variations of its direct current power supply source.

Another object of our invention is the provision of a regulating means suitable for use with an audio frequency over-lay track circuit which will maintain the receiver sensitivity substantially constant and independent of voltage variations of its direct current power supply source.

A further object of our invention is the provision of a regulating means capable of providing and maintaining either positive, negative or Zero regulation of the power out-put of an amplifier with respect to voltage variations of its direct current supply source.

Other objects, purposes and characteristic features of our invention will become apparent from the following description taken in connection with the accompanying drawings.

In practicing our invention, we employ a regulating transformer interposed within an amplifying system. The regulating transformer comprises a three legged core structure having dual section primary and secondary windings, each having one section mounted on an outside leg of the core structure, and a control winding mounted on the center leg of the core structure. The control winding is energized with direct current proportional to the voltage of the amplifiers direct current supply source. A capacitor is connected in shunt with the primary winding and resonated with the primary winding inductance to a frequency having a predetermined relationship with the operating frequency of the amplifying system.

We shall describe two forms of regulating apparatus embodying our invention, and shall then point out the novel features thereof in the appended claims.

In the accompanying drawings,

FIG. 1 is a diagrammatic view of an audio frequency overlay track circuit of the type employing a transmitter and a receiver embodying our invention for regulating the transmitter power output and the receiver sensitivity.

FIG. 2 is a schematic view of a transmitter suitable for use in connection with an overlay track circuit of the type shown in FIG. 1, and provided with regulating ap paratus embodying our invention for regulating the audio frequency power supplied to the track rails in the necessary manner to compensate for voltage variations of the transmitters power supply source.

FIG. 3 is a schematic diagram of a receiver suitable for use in connection with an audio frequency overlay track circuit of the type shown in FIG. 1 and provided 'with regulating apparatus embodying our invention for regulating the receivers sensitivity in the necessary mannor to compensate for voltage variations of the receivers power supply source.

FIGS. 4 and 5 are diagrams illustrating certain of the operating characteristics of the regulating apparatus embodying our invention.

Similar reference characters refer to similar parts in each of the several views.

Referring first to FIG. 1, the reference characters 1 and 1a designate the track rails of a stretch A of railway track. The nails 1 and 1a are divided by means of insulated joints 2 to form a plurality of track sections, only one of which B-C is shown complete in the drawings. Each track section is provided with a track circuit including a source of electrical energy here shown as a battery 3 connected across the track rails adjacent one end of the section, and means sensitive to the source of energy as, for example, a track relay designated by the reference character R connected across the rails adjacent the opposite end of the section. Trafiic entering each track section is governed by a signal D which may be of any suitable type, but which, in the form here shown,

is a two position semaphore signal capable of indicating either proceed or stop.

Located in section B-C is a manually operable track switch S which connects this section of track with a spur on siding E. The siding is insulated from section B-C by means of insulated joints 2, and the track rails between the insulated joints, leading to the track siding are cross bonded with the rails of section BC in the usual and well known manner. The switch S may be moved between normal and reverse positions by any suitable manually operated mechanism, not shown in the drawings. A lock bar F is rigidly secured to switch S for engagement by a dog G by means of which the switch can be locked in its normal position. The dog G is actuated by a manually operated lever H which is fixed to a shaft, as indicated by broken line 4, and which may be rocked between the normal and reverse positions as indicated by reference characters n and r, respectively.

A locking device, indicated as a whole by the reference character 1, comprises a locking segment 5 which is fixed to the shaft 4 and which is formed with a notch 6 for engagement with a latch 7. The latch 7 is controlled by a lock magnet I so that when the magnet is energized the latch will be lifted out of locking engagement with the segment 5 to permit shaft 4 to be operated for disengagement of the dog G from the lock bar F.

Lock magnet J is controlled by an audio frequency overlay track circuit comprising a transmitter 8, a receiver 11, and an associated section of railway such as the section of track between reference characters 13 and 14. Transmitter 8 supplies alternating current energy having a frequency of the order of 1000 cycles per second to the track rails l and 1a by means of connecting leads 9a and 9b. The audio frequency current flows through the track rails and receiver connecting leads 10a and 10b to receiver ll. Receiver 11 is connected to a relay 12 which remains energized as long as the audio frequency overlay track circuit is unoccupied. Relay 12 controls lock magnet I in such a manner that when lever H is in its normal position and the audio frequency track circuit is unoccupied lock magnet I will be deenergized to lock the switch in its normal position.

The overlay track circuit extends along the track in both directions and has an effective length which extends between the points marked with reference characters 13 and 14. The track circuit is restricted to these limits by means of our regulating apparatus. A train to the left of point 13 or to the right of point 14 is prevented from shunting the track circuit by virtue of the relatively high track impedance. However, a train shunting the track rails between points 13 and 14 bypasses suflicient energy away from the receiver so that relay 12 becomes deenergized. Relay '12 is made slow to pick up so that any momentary loss of shunt will not allow the relay to be energized. The release of relay 12 closes its back contact 15 and completes the circuit for energizing lock magnet I. This circuit may be traced from the positive terminal of battery 16 through back contact 15 of relay 12, conductor 17, lock magnet l and back to the battery through conductor 18. When the lock magnet J becomes energized it raises the control latch 7 to disengage it from locking engagement with segment 5. The unlocking of segment 5 permits the lever H to be manually shifted from position n to position r which unlocks switch S and permits it to be manually moved from the normal position shown to its reverse position.

The audio frequency overlay track circuit must be restricted from the area of switch S. That is to say, that the end of the track circuit indicated by reference character 13 must be prevented from extending beyond the switch. If it were permitted to do so sufficient current may flow into the siding rails, through the bonding connection between the rails of the tracksiding and the rails of the main track, to permit a car that may be shunting the siding rails between the insulated joints to shunt the audio frequency overlay track circuit. In this instance, switch I would be electrically unlocked and the control lever H could be moved to the reverse position. To prevent this condition it is necessary to provide the transmitter and receiver with means for maintaining the track circuit length constant which is the purpose of our regulating apparatus.

A transmitter suitable for use in connection with an audio frequency overlay track circuit of this type is shown in FIG. 2. Our regulating means is incorporated in the transmitter circuitry for regulating the transmitter power output so as to compensate for voltage variations of its direct current supply source, here shown as a battery 19. Although the source is shown as a battery, it should be understood that the source may, equally as well, be an alternating current source and a rectifier of any other suitable arrangement. Also the term positive, negative and zero regulation, as used herein, is defined to mean that the ratio of the difference between the amplifier power output with normal battery voltage and the power output after a change in the battery voltage to the power output after the change in battery voltage is positive, negative or zero, respectively.

Referring now to FIG. 2, the transmitter comprises an oscillator 20, amplifiers 21 and 27, a regulating transformer 24 and a battery 19. The oscillator 20* produces alternating current energy having a frequency within the audio frequency spectrum which is supplied to the input circuit of amplifier 21. The output circuit of amplifier 21 is connected to a primary winding, consisting of two identical coils 23a and 23b, mounted on a magnetizable core 26 of transformer 24. The transformer core is composed of a three legged structure having two outside legs and a middle leg. Each outside leg has one coil of the primary winding wound around it and the two coils are connected in a series aiding relationship. Similarly, a secondary winding, consisting of two identical coils 25a and 25b, has one coil located on each of the outside legs of the core. The secondary coils are connected in a series aiding relationship to the input circuit of amplifier 27. The output circuit of amplifier 27 is connected to the track rails 1 and 1a by means of conducting leads 9a and 912.

A capacitor 22 is connected in shunt with the primary winding to provide a parallel resonant circuit resonated to a frequency having a predetermined relationship with the transmitter operating frequency as explained hereinafter. Although we'have shown the capacitor as being connected in parallel with the primary winding it may equally as well be connected in shunt with the transformer secondary winding as indicated by capacitor 22a A control winding 28 located on the center leg of the transformer core is positioned so as to have symmetry with respect to the primary and secondary windings. The

control winding is connected through a series resistor 29 to the direct current supply source 19 and is thereby energized with a current proportional to the battery voltage. The flow of current through this winding establishes a magnetic biasing flux in the transformer core, and the inductance of the windings on the core is dependent upon the magnitude of the biasing flux. With this arrangement, the winding inductance can be adjusted to a predetermined value by the proper choice of resistor 29 which limits the flow of current in the control winding. The normal value of the resistor 29 is such that the primary winding will provide the necessary inductance to resonate with the capacitor at a frequency slightly higher than the transmitter operating frequency as illustrated in FIG. 4.

Referring now to FIG. 4, the impedance versus frequency curve of the parallel circuit comprising capacitor 22 and the primary winding, which we will hereinafter refer to as the resonant circuit, is shown as solid curve K. The natural resonant frequency of the resonant circuit and the transmitter operating frequency are indicated by reference characters f2 and 11, respectively. The

impedance of the resonant circuit at the transmitter operating frequency is indicated by reference character 30. Any variations of the battery voltage produce similar changes in the control winding current and the biasing flux in the transformer core. The change in the bias flux causes an inverse change in the primary Winding inductance. That is to say, an increase in the magnetic biasing flux decreases the winding inductances and vice versa. The effect of the inductance change upon the impedance curve is to shift the curve to the left or right as indicated by dotted curves L or M, respectively.

In order to understand the manner in which our regulating apparatus functions to maintain a substantially constant transmitter power output for variations of the battery supply voltage let it be assumed that the battery voltage decreases for some reasons such, for example, as aging of the battery. Without the use of our regulating apparatus this would decrease the power supplied to the track rails which would decrease the audio frequency overlay track circuit length. However, the reduced battery voltage also lowers the magnitude of the control winding current which, in turn, lowers the magnetic biasing flux in the transformer core. The resultant magnetic bias increases the primary winding inductance which lowers the natural resonant frequency of the resonant circuit and the impedance curve is shifted to the left as indicated by dotted curve L. Since the transmitter operating frequency remains substantially constant, the resonant circuit impedance increases from that indicated by reference character 30 to that indicated by reference character 31, and the increased impedance results in a larger voltage being developed across the primary winding. The increased primary Winding voltage produces an increase in the voltage induced in the secondary winding which is applied to the input of amplifier 27. The increased input voltage to the amplifier 27 increases the power delivered to the track rails and compensates for the reduced power output as caused by the reduced battery voltage. The control winding current and capacitor 22 may be chosen so that complete compensation may be attained and the audio frequency overlay track circuit length restored to normal.

Similarily, an increase in the battery supply voltage may be compensated for. If the supply source voltage increases as occurs, for example, when the battery is re placed with a new battery the power supp-lied to the track rails 1 and 1a would increase Which would increase the track circuit length. However, the increased battery voltage also increases the control winding current which in turn increases the magnetic bias in the transformer core and decreases the primary winding inductance. The decreased inductance increases the natural resonant frequency of the resonant circuit, which shifts the impedance curve to the right as indicated by the dotted curve M. This lowers the impedance of the resonant circuit, at the oscillator operating frequency, to that indicated by reference character 32 and lowers the voltage developed across the primary winding. The reduced primary winding voltage lowers the voltage induced into the secondary winding and the input signal voltage to amplifier 27. The reduction in the amplifier input voltage is just sufiicient to reduce the power delivered to the rails by the amplifier the necessary amount to compensate for the increased power output, as produced by the increased battery voltage, which restores the efiective length of the overlay track circuit to normal.

Referring now to FIG. 3, there is shown a receiver circuit suitable for use in connection with the audio frequency overlay track circuit. The receiver employs a regulating means similar to that described in connection with the transmitter and is used to maintain the receiver sensitivity constant. The receiver functions in basically the same manner as the transmitter with the exception that its input signal is obtained from the track rails rather than from an oscillatory stage and the receiver 6 power output is applied to a relay rather than to track rails. However, insofar as the operation of our regulating means is concerned, its operation is basically the same as that of the transmitter circuitry and, for that reason, it will not be given detailed consideration.

Heretofore, we have described and illustrated the manner in which our regulating apparatus may be employed to compensate for the supply battery voltage variations. The apparatus may be used, however, to overcompensate for these variations. In this case, resistor 29 and capacitor 22 are selected so that the impedance curve is relatively steep. This condition is best obtained by selecting the resistor so that only a small current flows through the control winding in order to make the primary winding Q relatively high. The capacitor is chosen so that the resonant frequency of the resonant circuit is related to the transmitter operating frequency as described heretofore. This condition allows the variations of the signal applied to the input of amplifier 27 to be larger than that necessary to just compensate for the supply battery voltage variations. Obviously, this amounts to negative regulation.

On the other hand, our regulating apparatus may be used to nndercompensate for the battery voltage variations in which case the control winding current is made relatively high so that a large magnetic bias is produced in the transformer core. In this instance, variations of the supply battery voltage have less effect upon the primary winding inductance and while compensation is provided, the supply battery voltage variations are not completely compensated for.

In many instances it is desirable that a system have a relatively high percentage regulation. Our apparatus is capable of providing such regulation in addition to zero or negative regulation, as described above. In this case capacitor 22 and resistor 29 are selected so that the self resonant frequency of the resonant circuit is lower than the operating frequency, as indicated in FIG. 5. Referring now to FIG. 5, curve N represents the impedance curve of the resonant circuit. The reference characters f1 and f2 represent the operating frequency and the self resonant frequency of the resonant circuit, respectively. The impedance of the resonant circuit at the operating frequency is indicated by reference character 33.

With this arrangement the supply battery voltage variations are emphasized which provides a high percentage regulation. A decrease in the battery potential results in a reduction in the power output from amplifier 27 more than that caused by the supply battery voltage variation itself. A decrease in the battery voltage decreases the control Winding current and the magnetic bias in the transformer core. This increases the primary Winding inductance and shifts the impedance curve to the left as indicated by dotted curve 0. However, with this arrangement the resonant circuit impedance decreases with a decreased battery voltage, whereas in the previous cases the impedance increased with a decreased battery potential. This lowers the resonant circuit impedance to that indicated by point 34 which decreases the primary winding voltage, secondary winding voltage and input signal voltage to amplifier 27 as described above. This decreases the power output of amplifier 27 more than that due to the drop in battery voltage alone.

An increase in the supply battery voltage is likewise emphasized. If the battery voltage increases, so does the control winding current and the magnetic bias which lowers the primary winding inductance and raises the natural resonant frequency of the resonant circuit. This shifts the impedance curve to the right as indicated by dotted curve P and the resonant circuit impedance is increased to that indicated by reference character 35. This increases the primary winding voltage, the secondary winding voltage, and the input signal voltage to amplifier 27. The increased amplifier voltage increases the amplifier output power above that produced by the increased battery voltage alone.

-It is therefore, obvious that our regulating apparatus may be used in connection with an amplifier to supply and maintain either positive, negative or zero regulation of the amplifier power output with respect to voltage variations of the amplifiers power supply source. Furthermore, the particular type of regulation desired will be sustained over a relatively wide range of voltage variations.

While in order to illustrate certain aspects of our invention we have shown an audio frequency overlay track circuit employing our regulating means, it is to be understood that the track rails merely function as conductors of a transmission system and insofar as the operation of I the circuit is concerned, they might be replaced by other forms of transmission conductors, such as line wires, within the scope of our invention.

While we have described two forms of our regulating apparatus as used in a transmitter and receiver employed with an audio frequency overlay track circuit, it is to be understood that various changes and modifications may be made therein without departing from the spirit and scope of the concluding claims.

Having thus described our invention, What we claim is:

1. Regulating means for regulating the output power of an amplifier energized by a source of direct current energy, said regulating means comprising a source of audio frequency energy energized by said source of direct current energy, a transformer provided with a primary winding connected to said source of audio frequency energy and a control winding connected to said source of direct current energy, a capacitor connected in shunt with said primary winding to provide a circuit resonated to a frequency having a predetermined relationship with the frequency of said source of audio frequency energy, and a secondary winding associated with said transformer and connected to the input circuit of said amplifier.

2. In combination in a track circuit including the usual track rails, a source of direct current energy, means for controlling the effective length of said track circuit including a transmitter having an output circuit connected to the rails of said track circuit, a receiver having an input circuit connected to the rails in spaced relation with the transmitter output connections, said transmitter including a source of audio frequency energy energized by said source of direct current energy, control means associated with said transmitter for regulating its power output, other control means associated with said receiver for regulating its sensitivity, said control means each including a transformer having primary and secondary windings the primary winding of the transformer associated with said transmitter being connected to the output of said source of audio frequency energy and the secondary winding of such transformer being connected to the output circuit of said transmitter, the primary winding of the transformer associated with said receiver being connected to the input circuit of said receiver and the secondary winding of such transformer being connected to the output circuit of said receiver, a capacitor connected in shunt with at least one of said primary and secondary windings of each of said transformers to provide a circuit with a resonant frequency having a predetermined relationship with the frequency of said audio frequency energy, and a control winding on each of said transformers connected to said source of direct current energy to control the impedance of said resonant circuits in accordance with the voltage of said source of direct current energy.

3. In combination in a track circuit including the usual track rails and a source of direct current energy, a transmitter and a receiver each arranged to be connected to said source of direct current energy, said transmitter including an output circuit connected to the track rails and including a source of audio frequency energy .energized by said source of direct current energy, means for regulating the power output of said transmitter including a transformer having a primary winding connected to the output circuit said source of audio frequency energy and a secondary winding connected to the output circuit of said transmitter, a capacitor connected in shunt with at least one of the windings of said transformer to provide a circuit whose resonant frequency has a predetermined relationship to the frequency of said source of audio frequency energy, and a control Winding on said transformer so connected to said source of direct current energy as to control the impedance of said resonant circuit in accordance with the voltage of said source of direct current energy, said receiver having substantially constant sensitivity and including an input circuit connected to the track rails in spaced relation to the output connections of said transmitter to said rails, and an indicating device energized by said receiver except when the track rails are shunted within a predetermined distance from the transmitter and receiver points of connection to said rails, said distance being controlled by the power output of said transmitter and the sensitivity of said receiver.

4. Regulating means for regulating the power output of an amplifier energized by a source of direct current energy by compensating for voltage variations in said source of direct current energy, said regulating means comprising a source of audio frequency energy energized by said source of direct current energy and having an output circuit; a transformer provided with a primary winding connected to the output circuit of said source of audio frequency energy, a control winding connected to said source of direct current energy, and a secondary winding connected to the input of said amplifier; and a capacitor connected in shunt with said primary winding to provide a circuit resonated at a frequency different from the operating frequency of said source of audio frequency energy, the current in said control winding being proportional to the voltage of said source of direct current energy, the resonant frequency of said circuit in turn being controlled by the current flow in said control winding, the impedance presented by said resonated circuit to said source of audio frequency energy being varied by any change in current through said control winding to compensate for any change in the voltage of said source of direct current energy.

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